This invention relates to controlling arrangement for a motor in the electrical drive system, more particularly, to that system used chiefly in an industrial sewing machine for the purpose of halting or stopping the machine and its needle at a certain preset position.
With regard to this sort of controlling arrangement, a conventionally practiced method of applying dynamic braking on the motor responding to a decelerating command for altering a high speed running down to a low speed running, and applying again, after having kept it running at the low speed for a while, the dynamic braking upon receiving a stopping command signal or employing an electromechanical braking means such as an electromagnetic brake, is known as a prior art of stopping a running motor for a sewing machine.
In this conventional method, it used to take a considerable length of time until the motor was completely stopped after a decelerating command signal had been produced, which was not a negligible factor with regard to efficient operation of industrial sewing machines and the like.
In the study of reasons for the delay, it was found that the period of time required for changing the speed from high to low after the command signal for the deceleration has been produced was the longest of all, i.e., the principal reason for the malefficiency of the conventional machines.